Magnetic transducer heads employing laminated assemblies or ferrite materials permit the attainment of heads having transducing gaps of very small length only with great difficulty, particularly in manufacturing. The high data recording densities required by modern day data processing demands very narrow transducing gaps in the sensing elements as well as extremely close-flying heights of these elements relative to the magnetic recording medium (nominally a high speed spinning magnetic disc). These desirable features are realized by fabricating a transducer head using thin film techniques and structures.
It is well known that using a magnetoresistive sensing element to read recorded data is highly desirable. A transducer head using a thin film magnetoresistive element is thin, affords savings in space, and may be batch fabricated with acceptable yields. In addition, such transducer heads are relatively inexpensive to fabricate. It is also well established that magnetoresistive sensors produce a substantially larger signal output than inductively reading heads at low velocities. The desirability of a transducer head having the dual capabilities of inductively recording data and magnetoresistively reading that data is recognized in U.S. Pat. No. 3,887,945 by Nepala et al, whose dual function head improves on the magnetoresistive read-only structures of U.S. Pat. Nos. 3,813,692 to Brock et al, and 3,814,863 to O'Day, et al. The present invention also relates to a transducer head that permits inductive recording (or writing) and magnetoresistive reading.
A brief explanation of the magnetoresistive effect will reveal why it is so desirable to read recorded magnetic data by a magnetoresistive sensor. Magnetoresistivity is the property of certain materials to exhibit a change in resistance in direct response to the magnetic flux to which the magnetoresistive element is exposed. Conventional inductive magnetic reading devices respond to the rate of change of magnetic flux. Hence, the output thereof is a function of the velocity of the recording medium. Thus, conventional magnetic reading heads are operable only over a narrow range of medium speeds. On the other hand, a magnetoresistive element will give a constant output over a wide range of recording medium speeds. This is important since the usual magnetic recording medium is a spinning disc whose velocity relative to the sensor changes substantially as the sensor moves across its face.
As noted by van Gestel, et al, in a paper entitled "Read Out of a Magnetic Tape By the Magnetoresistance Effect" (published in Philips Tech. Rev. 37, 42-50, 1977. Number 2/3), magnetoresistivity has been known since 1857, but only recently has its significance in magnetic recording been appreciated. The most important advantage, according to these writers, of reading recorded data out by means of variations in magnetoresistance lies in the possibility of making the reading head very small without reducing the sensitivity to an unacceptably low value.
In order to overcome the small sensitivity and to provide a linear transducer when the strength of the recorded magnetic field is small, it is desirable to provide a magnetoresistive element in which the current and the preferred direction of magnetization are at an acute angle (i.e., 30-60 degrees) with respect to each other. This may be achieved by the so called "barber pole" configuration in which the magnetoresistive element and the coil turn or turns thereabout resemble a barber pole. More precisely, to obtain the desired acute angle, the current is made to flow obliquely by covering the active area of the magnetoresistive element with one or more oblique conductive stripes. This technique is described by van Lier et al, in a paper entitled "Combined Thin Film Magnetoresistive Read, Inductive Write Heads" (IEEE Transactions on Magnetics, Volume MAG-12, No. 6, November, 1976).